This invention more particularly covers the area of systems capable of providing a connection between a spinal osteosynthesis rod and a crossbar.
In the state of the art, there are a number of known intervertebral connecting devices. In a conventional way, such a device includes bone anchoring elements such as, for example, peduncular implantation screws or vertebral hooks, each equipped with an attachment head for a connection rod joining these elements together. The bone anchorage elements are distributed along the area of the spinal column to be treated to permit the mounting of two connection shafts extending more or less in parallel to one another on either side of the spinal apophyses of the vertebrae. At least one cross strut between the connection rods is advantageously used to stabilize and/or achieve a corrective effect on the arrangement made (either in relaxation or in compression).
Different types of connection systems between an osteosynthesis rod and a crossbar have been proposed in the prior art. For example patent FR 2 745 708 describes a connection system consisting of a first jaw-shaped part with a channel for the crossbar and a lock screw that can extend into the channel, and a second part in the form of an opposing jaw hinged onto the first part. The channel is adapted to receive the transversal connection part which, when the screw is tightened, can come to rest against the first and second parts in order to bring the jaws together. Such a connection system has the advantage of being able to be adapted directly to spinal osteosynthesis rods at any point on the rods, except of course the installation sites of the peduncular screws and hooks. Moreover, the jaws of this system partially surround the osteosynthesis rod, which prevents local intervention on the vertebrae to clear the space needed to install this connection system.
However, it must be noted that the operation of installing this system connecting a crossbar and an osteosynthesis rod is very difficult to carry out properly. Indeed, one must recognize that the connecting system must be maintained on the osteosynthesis rod while making sure the crossbar slides through the reception channel. Maintenance of the system must be pursued in order to permit a slight tightening of the lock screw to make sure the connection system remains in position while retaining overall mobility in order to install another connection system at the opposite end of the crossbar.
To try to offset these drawbacks, document FR 2 771 918 proposed a connector for a spinal osteosynthesis device made in the form of a single piece designed to present two jaws extending by means of connections from a head for a crossbar to pass. Given the elasticity of the material and the slots made at the connections, the two jaws rotate freely to tighten the osteosynthesis rod. This connector is therefore clamped onto the rod before the crossbar is installed. However, the connector is adapted to the rod with a clamping force that is difficult to control given the way the jaws are made. It is therefore difficult to install and position the connector on the rod.
To achieve this objective, the connection system between a spinal osteosynthesis rod and a crossbar is set up in such a way as to offer a channel for the crossbar that is designed to exert an effort on two jaws hinge-mounted so as to make sure they will come together when a locking device is tightened. According to the invention, the connection system includes a common hinge pin to which the jaws are attached and a return spring mounted so as to work on the two jaws to bring them relatively close together independently of the crossbar in such a way that the jaws clamp the osteosynthesis rod in order to ensure the stable mounting of the connection system onto the said rod.